(Subscript[(OverHat[R]), 1])=(Underscript[arg min, A∈(Subscript[Θ, 1])])((\[LeftBracketingBar]trace((Subscript[R, 1])(A^H))\[RightBracketingBar])/(\[LeftDoubleBracketingBar](Subscript[R, 1])\[RightDoubleBracketingBar]\[LeftDoubleBracketingBar]A\[RightDoubleBracketingBar]))